Electromagnetic drive tuning fork reciprocating motor



c. D. o'NEAL 3,183,382 ELECTROMAGNET DRIVE TUNINQFORK RECIPROCATING MOTOR l May 11, 1965 Filed Aug. 15, 1962 ,tion on each tine, and a United States Patent C) 3,183,382 ELECTROMAGNETIC DRIVE TUNING FRK Y RECIPROCATING MG'ER Cleou D. ONeal, Deerfield, Ill., assigner to Motorola, Inc., Chicago, Ill., a corporation of Illinois Filed Aug. 15, 1962, Ser. No. 217,056 14 Claims. (Cl. S10-17) This invention relates to electromechanical resonant translating devices, and more particularly to such a device adapted for use in selective tone signalling apparatus for communication systems.

In selective tone signalling apparatus, a mechanically resonant structure may be utilized as the frequency controlling element for generator of a given tone signal, or as a frequency responsive device for controlling an operation in response to a given tone signal. A tone of a given frequency derived from a generator including such a resonant device may be transmitted by a radio or other transmitter, and such tone may be received and applied to a device responsive to that particular frequency for controlling any desired apparatus. Such devices must perform with proper sensitivity at only one frequency, have proper selectivity, operate within a predetermined time, and perform with stability of all functions over wide temperature ranges. Such a device must also provide isolation of the critical components from external shock and vibration influences.

With the trend to miniaturization, it has become desirable to construct such mechanically resonant devices which occupy a minimum of space without detrimentally affecting the qualities necessary for eflicient operation. For use in small portable communication units the resonant device must be correspondingly small. Known systems have a certain amount of inertial instability and this has become more pronounced when the stiffness of the supporting structure is reduced, especially at low frequencies.

Accordingly, it is an object of this invention to provide an electromechanical resonant translating device which can be provided as a miniature unit.

Another object of the invention is to provide an improved electromechanical translating device capable of reproducing a single tone, free of mechanical harmonics.

A further object of the invention is to provide an electromechanical translating device of sturdy construction and adapted to be mass produced in units varying over a wide frequency range.

Another object of the invention is to provide an electromechanical translating device of low mass having inertial and frequency stability over a wide temperature range.

Still another object of the invention is to provide an electromechanical translating device wherein performance characteristics may be varied by adjustments made during production.

A still further object of the invention is to provide a method for assemblying an electromechanical translating device having the above mentioned characteristics which method is rapid, accurate and inexpensive.

A feature of the invention is the provision, in an electromechanical translating device, of a tuning fork structure having a pair of tines with the core members extending extending from the juncture between the base blocks to a mounting post to resiliently support the tuning fork of windings.

Another feature of the invention is the provision of a tuning. fork structure having a pair of tines, a base por pin joining the base portions to form a unitary base for the tuning fork structure, and the further provision -of a leaf spring fixed to the pin and extending from the juncture between the base blocks to 3,l83,382 Patented May 11, 1 965 a mounting post toY resiliently support the tuning fork structure in position on a chassis.

Still another feature of the invention is the provision of an electromechanical translating device including a tuning fork having a rigid base portion and a damping structure engaging the base portion thereof.

A further feature of the invention is the provision of a method for assembling an electromechanical translating device having'the above-described structure, including the step of suspending the tuning fork tines in position with the cores extending therefrom centered in the windings, and then securing the base portions of the tines together and to a leaf spring to form a dynamically stabilized base supported from the rigid mounting post of the chassis by means of the leaf spring.

A still further feature of the invention is the provision, in an electromechanical translating device containing the above features, of a plurality of pins extending through the chassis and insulated therefrom, and having leads connecting the various elements of the structure electrically, with the leads and pins being secured in place by a resinous compound.

In the drawings:

FIG. 1 is atop plan view of a device constructed in accordance with the invention;

FIG. 2 is a sectional View taken along the line 2 2 of FIG. l showing a cover member in place with the cover and chassis in section, and a connection plug;

FIG. 3 is a front elevation thereof showing the cover member in place with the cover and chassis in Section;

FIG. 4 is an exploded view showing certain elements of the device; and

FIG. 5 is a top the invention.

In a particular form of the invention, a chassis is pro vided with a mounting post extending therefrom. A tun ing fork structure comprising a pair of tines, each having a base block fixed at one end thereof, is held in assembled condition by means of a pin embedded in the base blocks to join them together to form a continuous base portion for the tuning fork structure. A pair of coils are mounted on the chassis between the tines of the tuning fork structure. A core member extends from each of the tines near the end thereof opposite the base block, and into the center of the windings. The tuning fork structure is sef cured to the mounting post by means of a leaf spring which is connected to the embedded pin and extends from the juncture between the base blocks to the `mounting post to resiliently support the tuning fork structure in position, with each core member extending into one of the coils. Damping material is positioned to engage the base portion of the tuning fork and provide a damping system which absorbs most of the energies imparted to the base by the vibrating tines thus eliminating in phase harmonics of the tuning fork. Connection pins extend through the chassis and leads connect such pins to the coils and other elements of the translating device. These leads and pins are sealed in the chassis by means of a resinous compound.

When an activating current is applied to either one or both of the coils to provide a flux variation at the resonant frequency, the tuning fork structure will vibrate at resonance as desired. When a signal not of the resonant fre.y quency is applied to the coils, the tuning fork will be effectively damped with the result that the vibrations will not be sustained by the tuning fork.

The construction of a particular form of the invention is shown in FIGS. l through 3. A chassis 11 is provided with a mounting post 13 extending upwardly therefrom. A slot having a wide portion 15 and a narrow portion 17 is formed in post 13. A partition 19 of magnetic material extends forward from` post 13. Mounted to plan view of another embodiment of vtively.V Holes 4-1 and 43 chassis 11 on either side of partition 19 are a pair of coils 21 and 23 formed about coil forms 22' and 24, having a common hollow center 25 which extends through are mounted at one end of the tines 33 and 35 respec-y are formed respectively in base blocks 37 and 39, and a pin 45 is inserted in the holes 41 and 43 to secure base blocks 37 and 39 together. The pin is embedded in the base blocks by tiowing solder in the holes about the pin to join the blocks and form a continuous base portion for the tuning fork structure. A leaf spring 47 is secured to pin 45 and extends from the juncture between base blocks 41 atnd 43 forward between tines 33 and 35. The opposite end of leaf spring 47 is secured to mounting post 13 in the narrow portion 17 of the slot therein. By-so securingthe blocks on the leaf spring 47, the tuning fork structure is supported resiliently on rigid mounting post 13 with the tines 33 and 35 thereof extending so that the free ends are adjacent windings 21 and 23 respectively. A core member 49 extends inwardly from tine 33 into hollow center 25, and a similar core member 51 extends inwardly from the tine 35 intoV hollow center 25. The'core members are formed of a permanent magnetic material such as Alnico 5.

The device shown in FIGS. l through 3 is designed as a selective switch for use with a receiver in a selective signalling system. VIn so adapting the unit to this use, a threaded bracket 27 is mounted on and insulated from the end of partition 19 and an adjustable contact 29 is screwed therein. Adjustable contact 29 is designed for engagement by wire contact 31 to complete an electrical circuit. Wire contact 31 is mounted on tine 35 `and a hook 53 extends from tine 35 to conne and secure wire contact 31 in position. Hook 53 also performs a damping function on contact 31 to improve contact time. A pair of brackets 55 and 57 extend inwardly from tines 33 and 3S respectively, and provide a means for applying solder or similar material 59 to weight tines 33 and 35 to accurately control the resonant frequency of the tuning fork structure. f l Y vA plurality of interconnecting pins 61 extend through chassis 11 and leads, for example 63, Amay be attached theretoto connect various elements of the system electrically to the pins. Lead 63 and pins 61 are secured to chassis 11by means of an epoxy resin filler 62 which is poured into the chassis for protective purposes. As may be seen from FIG. 2, a pair of mounting lugs 64 are secured to the bottom of chassis 11. A plug 65 may be provided with'openings 67 and 69 to receive lugs 64 and pins 61 respectively. Solder connectors with integral electric contacts 71 may be provided Yto connect the frequency responsive device to other electricalapparatus by engagement with pins 61. Also shown 'in FIGS. 2 and 3 is cover 76 which snaps over the device for protecting the structure from dirt or moisture. The cover may be sealed on the chassis.

Because of certain physical phenomena involved, the tinesof the tuning fork structure at resonance (the frequency of operation) will vibrate out of phase. In consequence of the common supportingbase comprised of base blocks 37 and 39 yand pin 45, for the two tines of the tuning fork, a very stable mounting platform is created at resonance because the kinetic energy values are equal and opposite. Damping material 72, which may comprise a silicon rubber elastomer, is poured about the base of the tuning fork structure to aid in dampingvibrations not of the resonant frequency of the tuning fork. At all frequencies other than the. resonance frequency, the tines of the fork will'vibrate in phase, setting up vibration in the base. Such vibration will be adequately damped by material 72. As previously described, the base of the tuning fork is stable at resonance and the leases damping of the material does not affect the operation Yof the device, except to reduce or eliminate the adverse effects of vibrations from external sources. Coils 21 and 2,3 can be connected'to drive tines 33 and35 out of phase, insuring that sustainedvvibration will not occur at other frequencies. Y t n The Q of the coils may be reduced, if desired, for a particular application, by varyingthe composition of coil forms`22 and 24 to increasethe conductivity and the eddy currents therein. As eddy currents are increased, they buck the applied signal in the coils to reduce the Q. The eddy currents may also beY increased by enlarging the core members relative to the coil forms 22 and 24. The starting time of the unit (that is, the time Vit takes the amplitude of the tuning fork -to reach 62% of its peak), is determinable by the formula is fdr where ts is the starting time Yin milliseconds, and fo is the resonant frequency of the tuningy fork structure. From this `formula it may be readily seen that as Q is reduced, the starting time becomes less. Relatively short starting time is a highly desirable attribute of a resonant device in many applications.

The value of the Q ratio is also significant with respect to the effective bandwidth of driving frequencies to which the unit will respond. Theselectivity of the device may be verydiicult to maintain when the driving voltage is of low value,.as'is often the case in miniature equipment, such as when the battery powering the device is nearing the end of its useful life.' Construction of the device to be fully functional and responsive to a lower driving voltage will tend to increase the bandwidth requirement at frequencies to vwhich the device is responsive. However, the bandwidth may be narrowed by increasing the lQ. Thus, the ability to select the Q by varying the material in the coil form, or varying the size of the core members has the further advantage that the variation in bandwidth may be readily controlled to maintain the desired selectivity.

Referring now'to FIG. 4, a method )of assembling the structure ofthe invention has been developed which is rapid and efficient. Core members 49 and 51 are aligned in the hollow center 25 of windings 21 and'23, as by theuse of an appropriate iixture. When core membersV 49 and 51 .are properly positioned, spring 47 is placed in the narrow portion 17 ofthe slot inmounting post 13. Spring 47 is placed with slot 46 (FIG. 2) which is formed therein to receive pin 45, located at a given disv tance from chassis 11. Slot 46 will therefore determine the alignment of tines 33 and 35 relative to chassis 11.

' When'this has been accomplished, pin 45 is inserted in slot 46 and the blocks 37 and 39 are fixed on pin 45, which may be moved toward or away from post-13 -in slot 46 as required.. Spring 47'may be secured in place by iiowing solder into the narrow portion 17 and into the juncture at 73 to join the structure. The fixture may then be removed.

Finally, thedamping material is poured about the base kof the tuning fork to partially ll shell 75, see FlG. 2.l Such a procedure insures accurate assembly of the device,

and any subsequent variation in the resonant frequency requirements of the structure may ber-accomplished by adding or subtracting material 59 at the juncture between bracket members 55 and 57 and tines 33 and 35 respectively.

Referringr now to FIG. 5, a similar construction is shown with a few modifications. Here the leaf spring 47' is straight rather than curved as in FIGS. 1 and 4. Furtherrnore, the deviceV shown in FIG. 5. is adapted for use in a circuit where resonance/action only is used, and consequently the contacts 29 and 31 with associated supports are absent. This structure may be utilized in an oscillator circuit such as that shown in the patent to Peth No.

, 5 2,759,103. In such a case the coils 21 and 23 may be sections of a single coil. In cases where two separate coils are used the coils may have different characteristics, such as dilerent impedances to match circuit in which they are coupled.

It may therefore be seen that the construction of this device, as described and shown, readily adapts itself to miniaturization while not compromising the desired performance characteristics. It will operate at extremely low driving voltages While maintaining precision operation. It is rugged and capable of withstanding considerable external shock and vibration Without iniiuencing the functional operation of the device. The design is adapted to easy fabrication and assembly of parts wherein frequency requirements may vary over a wide range. Performance of a highly stable nature is possible Without encountering difiiculties from inertial instability, even at exceptionally low frequencies. Finally, the parts are adapted to certain simple alterations which may provide a wide adjustment of pertinent response characteristics, crucial to good performance in such selective signalling devices.

I claim:

l. An electromechanical translating device, including in combination, a supporting chassis, winding means mounted on said chassis, a tuning structure resonant at a predetermined frequency having elongated vibratory means and a base portion joined thereto at one end, said tuning structure being disposed with said vibratory means perpendicular to the axis of said winding means, permanent magnetic core means mounted on said vibratory means and extending therefrom to be suspended within said winding means, resilient means mounted on said chassis and xed to said base portion of said tuning structure to support said tuning structure in position relative to said winding means, and damping means engaging said base portion of said tuning structure, to provide a dynamically stabilized base portion for said tuning structure at said resonant frequency.

2. An electromechanical translating device, including in combination, a supporting chassis, first and second axially aligned coils mounted on said chassis, a tuning fork structure resonant of a given frequency and having first and second tines and a common base portion, said tuning forli structure being disposed so that said first tine is perpendicular to the axis of said first coil adjacent an end thereof and so that said second tine is perpendicular to the axis of said second coil adjacent an end thereof, a first core member on said first tine extending in a direction to be suspended Within said tirst coil, a second core member on said second tine extending therefrom opposite said first core to be suspended within said second coil, resilient means mounted on said chassis and xed to said b se portion of said tuning fork structure to support said tuning fork structure in position relative to said coils, and damping material engaging said base portion of said tuning fork structure to provide a dynamically stabilized base portion for said tuning fork structure at said resonant frequency.

3. An electromechanical translating device, including in combination, a supporting chassis, first and second axially aligned coils mounted on said chassis, a tuning fork structure resonant of a given frequency and having iirst and second tines and a common base portion, said tuning fork structure being disposed so that said iirst tine is perpendicular toA the axis of said first coil adjacent an end thereof and so that said second t-ine is perpendicular to the axis of said second coil adjacent an end thereof, a first permanent magnet core member on said first tine extending in a direction to be suspended within said iirst coil, a second permanent magnet core member on said second tine extending therefrom opposite said first core to be suspended within said second coil, and resilient means mounted on said chassis and fixed to said base portion of said tuning fork structure to support said tuning fork structure in coils.

4. An electromechanical translating device, including in combination, a supporting chassis, first and second coils mounted on said chassis and having a common axis, a tuning forli structure resonant at a given frequency and having a pair of tines and a common .base portion, said tuning fork structure being disposed with said coils between said tines `and With said tines perpendicular to the axis of said coils, a magnetic core member on each of said tines extending inwardly therefrom to ibe suspended within the adjacent one of said coils, resilient means mounted on said chassis and fixed to said base portion of said tuning fork structure to support said tuning vfork structure in position relative to said coils, and damping material engaging said base portion of said tuning fork structure to provide Ia dynamically stabilized base portion for said tuning fork structure at said resonant frequency.

5. An electromechanical translating device, including in combination, a supporting chassis having a mounting post thereon, a .coil form mounted on said chassis and having first and second coils Wound thereon with a common axis, a tuning fork structure resonant at a given frequency and comprising a pair of tines each having a `base block xed at one end thereof and a centrally embedded pin joining said base blocks to form a continuous base portion for said tuning fork structure, said tuning fork structure being disposed with said coils between said tines and with the axis of said coils perpendicular to said tines, a magnetic core member on each of said tines proximate the free end thereof and extending inwardly therefrom to be suspended within the adjacent one of said coils, a leaf spring fixed at one end to said pin and extending from the juncture between said base blocks and fixed at its other end to said mounting post to resiliently support said tuning fork structure in position relative to said coils, and a damping structure formed of silicon rubber elastomer and engaging said base portion of said tuning fork structure to provide a dynamically stabilized base portion Afor said tuning fork structure at said resonant frequency.

6. An electromechanical translating device, including in combination, a supporting chassis having a mounting post thereon, first and second coil forms mounted on said chassis and having first and second coils respectively wound'thereon with a common axis, a tuning fork structure resonant at a given frequency and comprising a pair of tines each having a lbase block fixed at one end thereof vand means joining said base blocks to form a continuous base portion for said tuning fork structure, said tuning fork strcuture being disposed with said coils between said tines and lwith the axis of said coils perpendicular to said tines, a magnetic core member on each of said tines proximate the free' end thereof and extending inwardly therefrom to be suspended within the adjacent one of said coils, a leaf spring fixed at one end to said base portion and fixed at its other end to said mounting post to resiliently support said tuning fork structure in position relative to said coils, a damping structure formed of silicon rubber elastomer and engaging said base portion of said tuning fork structure to provide a dynamically stabilized base portion for said tuning fork structure at said resonant frequency, a plurality of connecting members extending through said chassis for electrical connection to outside circuitry, and

position relative to said `a plurality of leads connecting said coils to said connecting members, lwith said connecting members and said leads 'being secured to said chassis by means of a resinous compound.

7. An electromechanical translating device, including in combination, a supporting chassis having a mounting post thereon, first and second coil forms mounted on said chassis and having first and second coils respectively wound thereon with a common axis, a tuning fork structure resonant at a given frequency and comprising a pair of tines each having a base block iixed at one end thereof and means joining said base blocks to form a continuous base aisasaa portion vfor said tuning fork structure, said tuning fork structure being disposed with said coils between saidtines and with the axis of said coils perpendicular to said tines, first contact means mounted on said base, second contact means mounted on one of said tines a given distance from said first contact means, said first and second contact means adapted to open and close according to vibration of said tines, a magnetic core member on each of said tines proximate the free end thereof and extending inwardly therefrom to be suspended within the adjacent one of said coils, a leaf spring fixed at one end to said base portion and fixed at its other end to said mounting -post to resiliently support said tuning fork structure in position relative to said coil-s, a damping structure formed of silicon rubber elastomer and engaging said base portion of said tuning fork structure to provide a dynamically stabilized base portion for said tuning fork structure at said resonant frequency, a plurality of connecting members extending through said chassis for electrical connection to outside circuitry, and a plurality of leads connectingr said coils to said connecting members, with said connecting members and said leads being secured to said chassis by means of a resinous compound.

8. A method of constructing an electromechanical translating device, including the steps of, providing a supporting chassis, securing winding means to the chassis, forming a pair of resonant tines each having a base portion at one end and a core member at the other end, centering the core members at given positions Within the winding means, holding the tines with the core members at said given positions within the winding means while securing the base portions of the tines together to form a tuning fork structure, and mounting the tuning fork structure on the chassis for vibration.

9. A method of constructing an electromechanical translating device, including the steps of, providing a supporting chassis, securing winding means to the chassis, forming a pair of resonant tines each having a base portion at one end and a core member at the other end, centering the core members at given positions within theY Winding means, holding the tines with the core members at said given positions within the winding means while securing the base portion of the tines together to form a tuning fork structure, mounting the tuning fork structure on the chassis for vibration, and providing damping material around the base portions of the assembled tuning fork structure in engagement therewith.

l0. A method of constructing an electromechanical translating device, including the steps of, providing a support chassis, securing winding means to the chassis, forming a pair of resonant tines each having a base portion at one end and a core member at the other end, centering the core members at given positions within the winding means, holding the tines with the core members at said given positions within the winding means while securing the base portions of the tines together to form a` tuning fork structure, mounting the tuning fork structure on the chassis for vibration, providing damping material around the base portions of the assembled tuning fork structure in engagement therewith, positioning connector elements with respect to the chassis, and pouring a resinous compound into the chassis to secure the connector elements thereto.

11. A method for assembling an electromechanical translating device having a chassis with a mounting post thereon, a tuning fork formed by a pair of tines each having a base block fixed at onerend thereof and a core member extending from the other end, and a supporting spring having a slot formed inY one end thereof, said method including the steps of, securing a pair of windings to the chassis, centering the core members at a given position within the windings, holding the tines by means of a fixture with the core members at said given positions within the windings Vsecuring the yend of the leaf spring opposite the slot to the mounting post, inserting a pin in the slot in the leaf spring, joining the base blocks together on the pin to form a suspended tuning fork structure with the spring extending from the juncture between the blocks to the mounting post, and forming a damping structure in engagement with the base portion of the tuning fork structure to damp extraneous vibration of the base portion of said tuning fork structure at the resonant frequency thereof.

12. A method for assembling an electromechanical translating device having a chassis with a mounting'post thereon, a tuning forkforrned by a pair of Ytines cach having a base block fixed at one end thereof and a core member extending from the other end, and a supporting spring having a slot formed in one end thereof, said method including the steps of, securing a pair of coil formshaving coils wound thereon Vto the chassis, centering the core members at a given position within the coils holding the tines by means of a fixture with the core members at said givenpositionsrwithin the coils whileV securing the end of the leaf spring opposite the slot to the mounting post with the slot at a given distance from the chassis, inserting a pin inthe slot in the `leaf spring, joining the base blocks together on the pin to form a suspended tuning fork structure with the spring extending from the juncturebetween the blocks-to the mounting posts, and forming a damping structure in engagement with the base portion of the tuning fork structure to damp extraneous vibration of the base portion of said tuning fork structure at the resonant frequency thereof.

13. An electromechanical translating device including in combination, a supporting chassis, winding means mounted on said chassis, a tuning structure resonant at a predetermined frequency having elongated vibratory means and a base portion joined thereto at one end, said tuning structure being disposed with said vibratory means perpendicular to the axis of said winding means, permanent magnet core means supported on said vibratory means and extending therefrom within said winding means, and mounting means for said tuning structure including resilient means mounted on said chassis and fixed ,to said base portion to support. said tuning structure, said mounting means including dampingmaterial engaging said base portion ofsaid tuning structure to provide a dynamically stabilized base portion for said tuning structure at said predetermined frequency.

14. The combination of claim 13, wherein said damping material is disposed about said base portion of said tuning structure and acts to damp vibrations not of the resonant frequency of said tuning structure.

References Cited bythe Examiner s UNrrED srArEs PATENTS V1,906,985. 5/33 Morrison 331-156 2,971,323 2/61 Heizel ssi- 156 V3,085,168 4/63 rousset a1. 33e-156 FOREIGN PATENTS 18,682 1901 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner. 

2. AN ELECTROMECHANICAL TRANSLATING DEVICE, INCLUDING IN COMBINATION, A SUPPORTING CHASSIS, FIRST AND SECOND AXIALLY ALIGNED COILS MOUNTED ON SAID CHASSIS, A TURNING FROK STRUCTURE RESONANT OF A GIVEN FREQUENCY AND HAVING FIRST AND SECOND TINES AND A COMMON BASE PORTION, SAID TURNING FORK STRUCTURE BEING DISPOSED SO THAT SAID FIRST TINE IS PERPENDICULAR TO THE AXIS OF SAID FIRST COIL ADJACENT AN END THEREOF AND SO THAT SAID SECOND TINE IS PERPENDICULAR TO THE AXIS OF SAID SECOND COIL ADJACENT AN END THEREOF, A FIRST CORE MEMBER ON SAID FIRST TINE EXTENDING IN A DIRECTION TO BE SUSPENDED WITHIN SAID FIRST COIL, A SECOND CORE MEMBER ON SAID SECOND TINE EXTENDING THEREFROM OPPOSITE SAID FIRST CORE TO BE SUSPENDED WITHIN SAID SECOND COIL, RESILIENT MEANS MOUNTED ON SAID CHASSIS AND FIXED TO SAID BASE PORTION OF SAID TUNING FORK STRUCTURE TO SUPPORT SAID TUNING FROK STRUCTURE IN POSITION RELATIVE TO SAID COILS, AND DAMPING MATERIAL ENGAGING SAID BASE PORTION OF SAID TURNING FROK STRUCTURE TO PROVIDE A DYNAMICALLY STABILIZED BASE PORTION FOR SAID TURNING FROK STRUCTURE AT SAID RESONANT FREQUENCY. 